Various abnormalities of the neurological system, such as brain and spinal tumors, cysts, lesions, or neural hematomas, can cause severe health risks to patients afflicted by them, including deterioration in motor skills, nausea or vomiting, memory or communication problems, behavioral changes, headaches, or seizures. In certain cases, resection of abnormal tissue masses is required. However, given the complexity and importance of the neurological system, such neurosurgical procedures are extremely delicate and must be executed with great precision and care.
Traditional tissue removal systems such as suction cannula, shavers and ultrasonic aspiration system have a predefined level of aspiration or vacuum delivered to the tip of the device. This predefined level of vacuum is usually defined by a vacuum source and may be either completely turned on or completely turned off. Some systems attempt to supply levels of vacuum somewhere in between the on and off configuration by creating a bleed hole for the vacuum supply that allows a portion of the vacuum to be bleed out of the inner cannula, thus reducing the level of vacuum supplied to the tip. A user may elect to cover a portion of the bleed hole by using the user's fingertip to cover all or a portion of the hole. By allowing the hole to be covered, only a portion of the vacuum supply is bleed through the hole, thus creating a level of vacuum less than the vacuum supplied by the vacuum source. However, this technique does not allow for a variable, reproducible level of vacuum.
Other tissue removal systems employ peristaltic systems. In peristaltic systems, a pump is set to a specific speed to generate vacuum. However, hysteresis that peristaltic systems exhibit provide difficulties to achieve instantaneous flow changes. For example, peristaltic pumps lack the ability to immediately vent vacuum pressure from a peristaltic pump system to atmosphere. Accordingly, when it becomes desirable to release tissue from a surgical device, for example when the instrument comes into contact with a critical structure, the operation of the peristaltic pump is not capable of immediately responding to a vent input. Instead, the operator is required to wait until the pump can adjust and necessary equilibrium of the system is restored. Such actions may result in surgeon fatigue during a surgical action, as well as potential damage to tissue where it is necessary to immediately release tissue.
Peristaltic pumps often also exhibit a pulsed flow, particularly at low rotational speeds of the peristaltic pump. Thus, peristaltic pumps are less suitable where a smooth consistent flow is required.